Pay close attention to how we pass in the current line number each time we run print_a_line.

What You Should See

Exercise 20 Session

$ python3.6 ex20.py test.txt
First let's print the whole file:
This is line 1
This is line 2
This is line 3
Now let's rewind, kind of like a tape.
Let's print three lines:
1 This is line 1
2 This is line 2
3 This is line 3